To obtain a clear and thorough characterization of normal, benign, and malignant human tissues, it is important for one to use a technique that can yield highly accurate broadband dielectric data with the flexibility to accommodate different shapes, sizes, and composition of tissues. Millimeter waves provide great accuracy and resolution to obtain characteristics of tissues over a broad frequency range.
Conventional solutions to detecting tumors, for example techniques described in U.S. Pat. No. 5,807,257 using back scatter radar techniques have not proven successful because back scattering techniques often lead to ambiguous results and are computationally expensive in order to achieve high resolution images.
Numerous dielectric techniques have been developed for detection of cancerous tissues. Early studies of the electric properties of tissues and cells proposed a method of employing induced electric and magnetic currents on the surface of tissues to analyze resonance scattering and subsequently characterize tumors. However, this technique has severe limitations with sample size, orientation, and frequency. Pulsed microwave confocal systems for early breast cancer detection with few micro-calcifications have been proposed. Unfortunately, this technique exploits the significant water content and enhanced scattering that occurs in the microwave range, thus limiting its detection capabilities to the microwave range.
Much of the dielectric spectroscopy work in cancer detection has been conducted in the microwave range. Measurements of cancerous tissue up to 20 GHz using an open-ended coaxial probe have been obtained. The dielectric properties of materials have been characterized in the past by many methods. However, microwave dielectric spectroscopy has several disadvantages. Probe and sensor measurements are extremely sensitive to surface level modulations and external environmental conditions. Unless caution is exercised, inaccurate interface between the probe and sample can distort results. Microwave techniques are also roughly limited in the spectra with an upper limit of 30 GHz and lower limit of 300 MHz.